Traditional airships, which may also be referred to as blimps, aerostats, dirigibles, or lighter-than-air vehicles, have an external skin made of numerous sections of fabric. Because of the size of the airship, the external skin must be formed from several sections of fabric that are joined by various seams. In such applications, a strap joint seam has been found to have acceptable durability, and resiliency to accommodate the operating requirements of the airship. To form the strap joint, at least two sections of fabric are arranged, such that the edges of each section of fabric are abutted or positioned closely adjacent one another to create a seam interface. Next, a layer of adhesive is applied to the region about the seam interface, and a tape or strap, is attached in a laminated manner to the adhesive layer. To complete the seam, heat and/or pressure may be applied to the strap, and fabric sections to allow the adhesive to melt, or flow, thus completing the formation of the seam. Once completed, forces or stress that are applied to the fabric sections are transferred through the tape of the seam, thus allowing the individual sections of fabric to behave as if it were a single section of fabric.
In general, traditional airships have used high elongation fabrics that also have a very high elasticity, or low-modulus. To form the completed skin of the airship, the fabric must be seamed together with other pieces of fabric, as previously discussed. As such, the structural longevity of the airship is dependent on the ability of the seams to distribute, and withstand the various forces applied thereto. Because the low-modulus fabric used on traditional airships is flexible, it allows forces that are imparted to the seam to be distributed to a suitable extent, rather than allowing forces to be concentrated in various regions of the seam. By preventing stress concentrations from developing at the seam regions, the airship is able to have a much longer operational lifespan, while increasing the time between seam repairs.
High-altitude airships, however, are designed to attain an altitude significantly greater than that of traditional airships. As such, different structural and mechanical considerations must be made, including the utilization of a high-modulus, high-tenacity, low-elongation fabric as an external skin. Unlike low-modulus fabrics used on traditional airships, high-modulus fabrics are highly resistant to stretching. Furthermore, high-tenacity fabrics are designed to rupture only when subjected to high levels of tensile stress. Because the skin of the high-altitude airship is subjected to various forces, some of which may be very high, the seams of the fabric sections of the external skin are also required to withstand such forces. However, because high-modulus fabric does not stretch sufficiently when loaded, stress is not distributed about the seam. Rather, stress from an applied load causes stress concentrations to develop locally in and about the area of the seam. This concentration of stress is unwanted, as it may lead to the premature failure of the fabric, and the seam that comprise the skin of the high-altitude airship, thus reducing its useful life.
Therefore, there is a need for a seaming system to join sections of high-modulus, high-tenacity, low-elongation fabric that reduces the concentration of stress in and about the region of the completed seam, so as to allow the seam to achieve enhanced load endurance. Additionally, there is a need for a seaming system to join sections of high-modulus, high-tenacity, low-elongation fabric that distributes stress along the length of the seam. Furthermore, there is a need for a seaming system that reduces the opportunity of de-lamination between the high-modulus, high-tenacity, low-elongation fabric, and the structural tape used to form the seam.